Satellite Shoot Down: How It Will Work

The U.S. Navy could shoot down an errant spy satellite as early as Wednesday night. Now a new computer model shows what might happen.

The spysatellite USA-193, also known as NROL-21, was launched aboard a Delta II rocketon Dec. 14, 2006 from Vandenberg Air Force Base in California. Shortly afterthe satellite reached orbit, ground controllers lost contact with it. Thoughthe satellite's objective is secret, many believe it is probably a high-resolutionradar satellite intended to produce images for the National ReconnaissanceOffice.

On Feb. 14,senior U.S. government officials at a Pentagon press briefing described a DefenseDepartment plan to try and shoot down the defunct satellite, after becomingconvinced that the spacecraft's toxic hydrazine fuel posed an unacceptable riskto people on the ground. The attempted strike could come Wednesday evening.

With thispress information, computer modelers Bob Hall and Tim Carrico at AnalyticalGraphics, Inc. (AGI) put together a computer-generatedsimulation of the missile-satellite collision. The model shows ahypothetical deployment of U.S Navy ships in the Northern Pacific Ocean and thefiring of a Standard Missile 3 at the failed satellite.

Informationthe modelers do know:

• The satellite has a mass of about 5,015 pounds (2,275 kilograms).
• The missile would be fired from a ship in the North Pacific Ocean.
• The interception would occur at an altitude of about 149 miles (240 kilometers).
• The satellite and missile would close on one another at a velocity of about 22,783 mph (36,667 kph).

If leftalone, the satellite is expected to re-enter Earth?s atmosphere some time betweenthe end of February and early March. About 2,500 pounds (1,134 kilograms) ofsatellite material would survive re-entry (the rest would burn up), including1,000 pounds (453 kilograms) of hydrazine, according to a statement from theU.S. Department of Defense.

Thecollision between the fired missile and the satellite would not only break themassive hunk of metal into pieces but would also speed up its tumble throughEarth's atmosphere.

"Ifyou want to bring something down, you slow it down. You apply a force on itwhich results in it being slowed down and decrease in its orbit," Carricotold SPACE.com. "Right at that point where they want to engage [the satellite] is atthe edge of the atmosphere, so you're bringing it down faster."

The plancomes on the heels of the intentional destruction last year of China'sFengyun-1C weather satellite, which produced a flurry of concern over thehostile-or-not nature of the firing as well as a serious load of shrapnellittering Earth orbit. That debris is still in space, frustrating missionmanagers and satellite operators forced to dodge the potentially debilitatingbits.

USA-193 isalready on its way toward Earth and the interception will take place at a muchlower altitude than that of the China satellite, presumably meaning thatwhatever happens, there will not be a fresh load of small junk sent intoperpetual orbit.

If moredetails were made public, the model results could change depending on severalfactors, including the location of the ships and when the missile is fired.

"Howthe missile hits the satellite will affect how quickly the debris re-enters andwhat the velocity is between the objects and how they hit," Hall said."Are they attempting to get most of the debris to come down in the Pacificalmost immediately? Or ... over the course of two or three revolutions, is mostof it going to start to fall out? If we had different information about theengagement we could re-run our model.

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